This invention relates to a process for polymerizing cis-1,3-pentadiene to an elastomer having a very high cis-1,4-polypentadiene configuration. The polymerization is catalyzed using a mixture of (A) a soluble chromium compound, (B) organometallic compounds, such as trihydrocarbylaluminums, dihydrocarbylmagnesiums or dihydrocarbylzincs, and (C) a dihydrocarbyl hydrogen phosphite.
1,3-PENTADIENE MONOMER EXISTS IN TWO FORMS, NAMELY, AS THE CIS- AND THE TRANS- ISOMERS. Each monomeric unit when polymerized contains at least one asymmetric carbon atom. There, theoretically, are 11 possible stereoregular polypentadienes.
U.S. Pat. No. 4,048,418 describes a process for polymerizing cis-1,3-pentadiene, using an iron catalyst system, to produce a polymer analyzing 93% cis-1,4-polypentadiene and which has a largely isotactic crystalline configuration; the same iron catalyst polymerizes trans-1,3-pentadiene to a syndiotactic trans-1,2-polypentadiene.
It is reported in Journ.Polym.Sci. 51, 463 (1961) that a vanadium catalyst polymerizes cis-1,3-pentadiene to isotactic trans-1,4-polypentadiene. The cis-1,3-pentadiene monomer is not polymerized by either cerium, cobalt or titanium catalysts although these catalyst systems do polymerize the trans-isomer.
U.S. Pat. No. 3,300,467 describes the polymerization of trans-1,3-pentadiene to polymers analyzing 65 to 87% cis-1,4-polypentadiene while using a titanium catalyst; and it is reported in Europ. Polym. Journ. 9, 189 (1973) that the titanium catalyst will isomerize the cis-1,3-pentadiene to trans-1,3-pentadiene and then polymerize the trans-monomer to a polymer containing 65 to 70% cis-1,4-polypentadiene.
U.S. Pat. Nos. 3,429,940 and 3,804,913 describe processes, using a ternary catalyst comprising a chromium compound, triethylaluminum and an alkyl halide, which oligomerize conjugated diolefins such as isoprene or piperylene to form cyclic trimers such as trimethylcyclododecatriene.
U.S. Pat. No. 3,754,048 describes a process that produces liquid polypentadiene while utilizing chromium acetylacetonate, a trialkylaluminum and a Schiff base as a catalyst system.
Japanese Patent No. 73 06,939 [see Chem. Abs. 80, 4644n (1974)] describes a process for polymerizing 1,3-butadiene to a polymer in which 95% of the unsaturation is 1,2-polybutadiene, while utilizing a ternary catalyst consisting of a chromium compound, an organoaluminum compound and a phosphoric acid ester.
Japanese Patent No. 73 64,178 [Chem. Abs. 80, 109590v (1974)] reports the preparation of 1,2-polybutadiene by polymerizing butadiene in the presence of hydrogen using as catalysts chromium acetylacetonate, dibutylphosphonate and triisobutylaluminum.
Thus, there is no prior art concerning the polymerization of cis-1,3-pentadiene by chromium-containing catalysts to prepare either any high cis-1,4-polydiolefins or any solid polypentadiene elastomers of any configuration.